1. Field of the Invention
This invention relates to rotary valves of brass instruments which change over lengths of resonance tubes to produce brass sounds of different pitches.
2. Prior Art
Brass instruments such as horns and trombones are equipped with rotary valves by which resonance tubes are changed over in lengths to produce brass sounds of different pitches. The mechanisms and operations of the rotary valves are disclosed by the paper of Japanese Patent Laid-Open Publication No. 1-280797 as well as the papers of Japanese Utility-Model Publication No. 3-2953 and Japanese Utility-Model Publication No. 59-13652, for example. Herein, the rotary valve is equipped with a certain number of change-over paths (simply, "paths") which are arranged on a peripheral surface of a rotor. A lever is manipulated to rotate the rotor, so it is possible to change over the paths.
FIGS. 6, 7 and FIGS. 8A to 8D show a conventioal example of the rotary valve equipped with the change-over paths. FIG. 6 is a side view with a partial cross section which shows a rotary valve 1. FIG. 7 is an exploded sectional view of the rotary valve. FIGS. 8A and 8B are cross sectional views taken along the line A-A'in FIG. 7; and FIGS. 8C and 8D are cross sectional views taken along the line B-B'in FIG. 7. Herein, FIGS. 8A to 8D show change-over states of the paths. The rotary valve 1 is constructed using a valve casing 2, a rotor 3, a lever 4, change-over paths 5 (specifically, 5a to 5d) and ports 6 (specifically, 6a to 6h). At first, the leverl 4 is manipulated to rotate the rotor which is inserted in the valve casing 2 and is capable of rotating freely. So, it is possible to change over the paths 5 of the rotor 3. Thus, the paths 5 are arbitrarily connected to the ports 6 of the valve casing 2.
The valve casing 2 has a cylinder-like shape whose both ends are open. There are provided eight ports 6a to 6h on a peripheral surface of the valve casing 2. The ports are subjected to two-stage arrangements in an axial direction of the valve casing 2. That is, four ports 6a to 6d are arranged in a upper stage with different phases, a difference of which corresponds to 90.degree.. In addition, other four ports 6e to 6h are arranged in a lower stage with difference phases, a difference of which corresponds to 9020 . Within the four ports 6a to 6d of the upper stage, a retractable tube 7 (not shown) is connected to the ports 6a and 6c whilst a resonance tube 8 (not shown) is connected to the ports 6b and 6d. Similarly, within the four ports 6e to 6h, a retractable tube is connected to the ports 6e and 6g while a resonance tube is connected to the ports 6f and 6h. An implantation bottom 10 is formed to engage with an upper opening of the valve casing 2. The implantation bottom 10 is provided to press an implantation bottom cover 9 to an upper face of the rotor 3. The implantation bottom cover 9 constructs a member to regulate movement of the rotor 3 in its axial direction. In addition, the implantation bottom cover 9 constructs a bearing member for the rotor 3 by a bearing hole 9a. Herein, a shaft portion 3A which projects from the center of the upper face of the rotor 3 is inserted to engage with the shaft hole 9a. An implantation upper cover 12 is provided to engage with a lower opening of the valve casing 2. The implantation upper cover 12 is connected to the valve casing 2 by soldering and the like. In some cases, the implantation upper cover 12 is manufactured together with the valve casing 2 by the integral cutting technique. The implantation upper cover 12 constructs a bearing member for the rotor 3 as well. So, the implantation upper cover 12 has a shaft hole 12a into which a shaft portion 3B of the rotor 3 is inserted. Herein, the shaft portion 3B which projects from the center of a lower face of the rotor 3 engages with the shaft hole 12a in a free rotation manner.
The rotor 3 is formed in a cylindrical shape. The change-over paths 5a to 5d are grooves which are formed on a peripheral surface of the rotor 3. Herein, a cross section of the path has a semicircular shape or a letter-U-like shape. The paths are subjected to two-stage arrangements in an axial direction of the rotor 3. So, the paths 5a and 5b are arranged in an upper stage with different phases, a difference of which corresponds to 180.degree.. In addition, the paths 5c and 5d are arranged in a lower stage with different phases, a difference of which corresponds to 180.degree.. As a result the change-over paths 5a to 5d are arranged to face with the ports 6a to 6h of the valve casing 2 respectively. The shaft portion 3B which projects downwardly from the lower face of the rotor 3 penetrates through the shaft hole 12a of the implantation upper cover 12 so that the shaft portion 3B partially projects downwardly from the cover 12. A projecting portion of the shaft portion 3B engages with a rotation base 13. Herein, it is securely fixed to the rotation base 13 by a screw 15. A stopper 14 is provided between the implantation upper cover 12 and the rotation base 13 to regulate an angle of rotation of the rotation base 13. The stopper 14 has a letter-C-like shape in a plan view. In addition, a cylindrical portion 16 projects downwardly from a lower face of the implantation upper cover 12. The stopper 14 engages with an outer periphery of the cylindrical portion 16. So, the stopper 14 is securely fixed to the implantation upper cover 12 by two screws 17. Further, two stopper rubber members 19 are attached to a lower face of the stopper 14 with different phases, a difference of which corresponds to 180.degree.. The two stopper rubber members 19 are provided to cope with a pin 18 which projects upwardly from an upper face of the rotation base 13. As described above, the two stopper rubber members 19 are arranged with different phases which differ by approximately 180.degree., while the pin 18 having a certain outer diameter is located between the two stopper rubber members 19. As a result, an angle of rotation of the rotation base 13 is set at 90.degree..
A lever support 22 is fixed to an outer periphery of the valve casing 2 through a lever fixing mount 21. The lever 4 is supported by the lever support 22 in such a way that it can rotate freely in up/down directions. In addition, a spring 23 imparts restoration behavior to the lever 4 in an upward direction. A lower end of the lever 4 contacts with one end of a lever connection rod 24 which transmits motion of the lever 4 to the rotation base 13. Another end of the lever connection rod 24 interconnects with a specific location of the lower face of the rotation base 13 via a rod end bearing 25. Herein, the specific location is eccentric from a center of the rotation base 13.
A normal state of the rotary valve 1 is shown by FIGS. 8A and 8B, wherein FIG. 8A shows a relationship between the paths 5a, 5b and the ports 6a to 6d in the upper stage while FIG. 8B shows a relationship between the paths 5c, 5d and the ports 6e to 6h in the lower stage. Herein, the path 5a interconnects the port 6a with the port 6b; the path 5b interconnects the port 6c with the port 6d; the path 5c interconnects the port 6e with the port 6f; and the path 5d interconnects the port 6g with the port 6h. Under the normal state, a human operator manipulates the lever 4 to rotatably move against the force of the spring 23, so that a lower end of the lever 4 depresses the lever connection rod 24. Thus, the lever connection rod 24 moves in a right direction in FIG. 6; and consequently, the rotation base 13 rotates by an angle of 90.degree.. As a result, the rotor 3 rotates together with the rotation base 13 to change over the paths 5a to 5d. FIGS. 8C and 8D show a state of the rotary valve 1 in which rotation of the rotor 3 completes. Herein, the path 5a interconnects the port 6a with the port 6c; the path 5b interconnects the port 6b with the port 6d; the path 5c interconnects the port 6e with the port 6g; and the path 5d interconnects the port 6f with the port 6h.
In the rotary valve 1 of the conventional example described above, all of the sliding portions are subjected to surface contacts (or sliding friction), so an amount of friction should be large. For this reason, relatively large force should be required to change over the paths 5. This raises a problem in manipulation of the rotary valve 1. In addition, abrasion may occur on parts of the rotary valve 1 due to the long-term usage. In that case, the rotor 3 may be subjected to floating phenomenon; and breath applied to the brass instrument may leak. This causes a problem that noise occurs in sound of the brass instrument. The conventional manufacturing method performs wrapping on an inner peripheral surface of the valve casing 2, an outer peripheral surface of the rotor 3, the shaft portions 3A, 3B as well as the shaft hole 9a of the implantation bottom cover 9 and the shaft hole 12a of the implantation upper hole 12, wherein gauging is made to provide a sufficient precision. This method suffers from a problem that manufacturing of the valve casing 2, rotor 3, implantation bottom cover 9 and implantation upper cover 12 is complicated. Particularly, it is necessary to finish the manufacturing of the rotary valve 1 such that a clearance between the inner peripheral surface of the valve casing 2 and the outer peripheral surface of the rotor 3 is made larger than a clearance between the shaft portion (i.e., 3B and 3A) and shaft hole (i.e., 12a and 9a). So, it is necessary to change grading of wrap materials. Herein, the precision of the conventional rotary valve depends on machine work accuracy as well as other factors. That is, the precision of the rotary valve is affected by the grading of the wrap materials, time of wrapping and a number of times to carry out the wrapping, so it may change by some chance. Therefore, it is difficult to provide stability in manufacturing quality of the rotary valve. To obtain a sufficient precision for the implantation bottom cover 9 in an axial direction, at a final assembly adjustment mode, it is necessary to lastly perform adjustment on so-called `L` measurements of FIG. 7. However, such adjustment causes the manufacturing cost of the rotary valve 1 to be higher.